Centrifugal compressor

ABSTRACT

A centrifugal compressor includes a rotary shaft, an electric motor, which has a rotor, a tubular boss, through which the rotary shaft extends, and a radial bearing. The rotor has a rotor end face, which is an end face in an axial direction of the rotary shaft. The boss has a boss end face, which is an end face in the axial direction of the rotary shaft. The rotor end face and the boss end face face each other in the axial direction of the rotary shaft. A thrust bearing is arranged between the rotor end face and the boss end face to receive thrust force generated by rotation of the impeller.

TECHNICAL FIELD

The present invention relates to a centrifugal compressor.

BACKGROUND ART

A centrifugal compressor includes, for example, a rotary shaft, an electric motor that rotates the rotary shaft, an impeller that compresses fluid by rotating with the rotation of the rotary shaft, a housing that accommodates the rotary shaft, the electric motor, and the impeller. For example, refer to Patent Document 1. Patent Document 1 also describes that a centrifugal compressor has a flange portion as a thrust liner, which integrally rotates with the rotary shaft, and two thrust bearings, which hold the flange portion in between.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Laid-Open Patent Publication No. 2009-257165

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

Since the thrust liner rotates as the rotary shaft rotates, windage loss occurs at the thrust liner. For this reason, there is a concern that the efficiency of the centrifugal compressor will be degraded.

Accordingly, it is an objective of the present invention to provide a centrifugal compressor that is capable of improving efficiency.

Means for Solving the Problems

To achieve the foregoing objective, a centrifugal compressor is provided that includes a rotary shaft, an electric motor, which includes a rotor attached to the rotary shaft and rotates the rotary shaft, an impeller, which rotates as the rotary shaft rotates, thereby compressing fluid, a housing, which accommodates the rotary shaft, the electric motor, and the impeller, a tubular boss, which is provided in the housing and through which the rotary shaft extends, and a radial bearing, which is provided between the boss and the rotary shaft and rotationally supports the rotary shaft. The rotor has a rotor end face, which is an end face in an axial direction of the rotary shaft. The boss has a boss end face, which is an end face in the axial direction of the rotary shaft. The rotor end face and the boss end face face each other in the axial direction of the rotary shaft. The centrifugal compressor includes a thrust bearing, which is arranged between the rotor end face and the boss end face and receives thrust force generated by rotation of the impeller.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically illustrating a centrifugal compressor and a vehicle air conditioner.

FIG. 2 is an enlarged cross-sectional view showing the rotor and the thrust bearing.

FIG. 3 is a cross-sectional view schematically illustrating a vehicle air conditioner according to a modification.

MODES FOR CARRYING OUT THE INVENTION

Hereinafter, a centrifugal compressor according to one embodiment will be described with reference to the drawings. In the present embodiment, the centrifugal compressor is mounted in a vehicle. For the illustrative purposes, a rotary shaft 12 is shown in the side view in FIGS. 1 to 3. Also, for the illustrative purposes, the thicknesses of magnetic steel sheets 51, holding plates 52, 53, spacers 55, 56, and thrust bearings 91, 92 are shown to be different from the actual dimensions.

As shown in FIG. 1, a centrifugal compressor 10 has a housing 11, which constitutes the outer shell thereof. The housing 11 has a substantially cylindrical shape as a whole. The housing 11 is made of a material having heat conductivity such as metal.

The centrifugal compressor 10 includes, as components accommodated in the housing 11, a rotary shaft 12, an electric motor 13, which rotates the rotary shaft 12, and first and second impellers 14, 15, which are attached to the rotary shaft 12. The rotary shaft 12 has a main body 12 a and a distal end portion 12 b, which has a smaller diameter than the main body 12 a and to which the first and second impellers 14, 15 are attached.

The housing 11 includes a front housing member 20. The front housing member 20 defines first and second impeller chambers A1, A2, which respectively accommodate the first and second impellers 14, 15. The front housing member 20 is composed of three parts 21 to 23. The parts 21 to 23 are unitized by holding the middle part 23 in between by the first part 21 and the second part 22 in the axial direction Z of the rotary shaft 12.

The first part 21 substantially has a tubular shape having a first compressor through-hole 21 a, which extends in the axial direction Z through the rotary shaft 12. The first part 21 has first and second end faces 21 b, 21 c, which are positioned on the opposite sides in the axial direction Z of the rotary shaft 12. The first compressor through-hole 21 a opens in the first and second end faces 21 b, 21 c of the first part 21. The first end face 21 b of the first part 21 contacts the middle part 23. The first compressor through-hole 21 a is shaped as a truncated cone the diameter of which gradually decreases from the opening in the first end face 21 b to an intermediate position in the axial direction Z of the rotary shaft 12. The first compressor through-hole 21 a has a columnar shape the diameter of which is constant from the intermediate position to the opening in the second end face 21 c.

The second part 22 substantially has a tubular shape the axial direction of which coincides with the axial direction Z of the rotary shaft 12. The second part 22 has first and second end faces 22 a, 22 b, which are positioned on the opposite sides in the axial direction Z of the rotary shaft 12. The first end face 22 a of the second part 22 contacts the middle part 23. A recess 22 c is provided in the second end face 22 b. A second compressor through-hole 22 d is provided in the bottom of the recess 22 c. The second compressor through-hole 22 d extends in the axial direction Z of the rotary shaft 12 through the bottom of the recess 22 c. The second compressor through-hole 22 d is shaped as a truncated cone the diameter of which gradually decreases from the opening that faces the middle part 23 to an intermediate position in the axial direction Z of the rotary shaft 12. The second compressor through-hole 22 d has a columnar shape the diameter of which is constant from the intermediate position to the opening of the middle part 23.

The middle part 23 is substantially shaped as a disc the thickness direction of which coincides with the axial direction Z of the rotary shaft 12. The middle part 23 has a first middle part end face 23 a and a second middle part end face 23 b. The first middle part end face 23 a contacts the first end face 21 b of the first part 21. The second middle part end face 23 b is located on the opposite side to the first middle part end face 23 a and contacts the first end face 22 a of the second part 22. The inner surface of the first compressor through-hole 21 a and the first middle part end face 23 a define a first impeller chamber A1. The inner surface of the second compressor through-hole 22 d and the second middle part end face 23 b define a second impeller chamber A2. That is, the middle part 23 partitions the first impeller chamber A1 and the second impeller chamber A2 from each other.

The middle part 23 has a middle part through-hole 23 c, through which the rotary shaft 12 is inserted. The distal end portion 12 b of the rotary shaft 12 is arranged to extend through the middle part through-hole 23 c and is arranged across the two impeller chambers A1, A2. A first impeller 14 is attached to part of the distal end portion 12 b of the rotary shaft 12 that is arranged in the first impeller chamber A1. A second impeller 15 is attached to part of the distal end portion 12 b of the rotary shaft 12 that is arranged in the second impeller chamber A2.

The first impeller 14 is substantially shaped as a truncated cone the diameter of which gradually decreases from a proximal end face 14 a toward a distal end face 14 b and is arranged in the first impeller chamber A1 along the inner surface of the first compressor through-hole 21 a. Likewise, the second impeller 15 is substantially shaped as a truncated cone the diameter of which gradually decreases from a proximal end face 15 a toward a distal end face 15 b and is arranged in the second impeller chamber A2 along the inner surface of the second compressor through-hole 22 d. The proximal end faces 14 a, 15 a of the impellers 14, 15 are opposed to each other.

The front housing member 20 (specifically, the first part 21) has a first suction port 30, through which fluid is drawn in. The first suction port 30 opens in the second end face 21 c of the first compressor through-hole 21 a. That is, the first compressor through-hole 21 a constitutes the first suction port 30 and the first impeller chamber A1. The fluid drawn in from the first suction port 30 flows into the first impeller chamber A1.

As shown in FIG. 1, the front housing member 20 has a first diffuser passage 31 and a first discharge chamber 32. The first diffuser passage 31 is arranged outward of the first impeller chamber A1 in the radial direction of the rotary shaft 12. The first discharge chamber 32 communicates with the first impeller chamber A1 via the first diffuser passage 31. The first diffuser passage 31 has an annular shape that surrounds the first impeller 14. The first discharge chamber 32 is arranged outward of the first diffuser passage 31 in the radial direction of the rotary shaft 12 and communicates with a first discharge port 33 provided in the front housing member 20.

Likewise, the front housing member 20 has a second diffuser passage 34 and a second discharge chamber 35. The second diffuser passage 34 is arranged outward of the second impeller chamber A2 in the radial direction of the rotary shaft 12. The second discharge chamber 35 communicates with the second impeller chamber A2 via the second diffuser passage 34. The fluid in the second discharge chamber 35 is discharged from a second discharge port 36 provided in the front housing member 20.

As shown in FIG. 1, the housing 11 includes a motor housing 41 and an end plate 42, which define a motor chamber A3 that accommodates the electric motor 13.

The motor housing 41 has a tubular shape with one end closed that has, for example, a bottom portion 41 a and opening on the side opposite to the bottom portion 41 a. The axial direction of the motor housing 41 coincides with the axial direction Z of the rotary shaft 12. The end plate 42 is shaped as a disc the diameter of which is equal to the outer diameter of the motor housing 41. The thickness direction of the end plate 42 coincides with the axial direction Z of the rotary shaft 12. The motor housing 41 and the end plate 42 are assembled with the open end of the motor housing 41 abutting against a first plate surface 42 a of the end plate 42. The open end of the motor housing 41 is closed by the end plate 42. The motor chamber A 3 is defined the motor housing 41 and the end plate 42.

The rotary shaft 12 extends through the bottom portion 41 a of the motor housing 41. The bottom portion 41 a has bottom through-holes 41 b, which allow the motor chamber A3 and the second impeller chamber A2 to communicate with each other. The bottom through-holes 41 b are arranged across both the portion of the bottom portion 41 a of the motor housing 41 that overlaps with the main body 12 a as viewed from the axial direction Z of the rotary shaft 12 and a portion surrounding that overlapping portion. The bottom through-holes 41 b overlap with the recess 22 c of the second part 22 as viewed from the axial direction Z of the rotary shaft 12. The motor chamber A3 and the second impeller chamber A2 communicate with each other via the bottom through-holes 41 b and the recess 22 c of the second part 22. The bottom through-holes 41 b are not continuously provided over the entire circumference of the rotary shaft 12 but are spaced apart at predetermined intervals in the circumferential direction of the rotary shaft 12.

As shown in FIG. 2, the electric motor 13 has a rotor 50 attached to the rotary shaft 12 (more specifically, to the main body 12 a of the rotary shaft 12). The rotor 50 has a tubular shape (specifically, a cylindrical shape) as a whole and the axial direction of the rotor 50 is the axial direction Z of the rotary shaft 12. The rotor 50 has first and second rotor end faces 50 a, 50 b, which are positioned on the opposite sides in the axial direction Z of the rotary shaft 12. The rotor 50 includes magnetic steel sheets 51 laminated in the axial direction Z of the rotary shaft 12 and first and second holding plates 52, 53, which hold the magnetic steel sheets 51 in between in the axial direction Z of the rotary shaft 12. The first and second holding plates 52, 53 make a pair. In the present embodiment, the magnetic steel sheets 51 and the first and second holding plates 52, 53 have the same shape, which is an annular shape as viewed from the axial direction Z of the rotary shaft 12. For the illustrative purposes, the side toward the magnetic steel sheets 51 in the axial direction Z of the rotary shaft 12 will be referred to as the inner side, and the side away from the magnetic steel sheets 51 in the axial direction Z of the rotary shaft 12 will be referred to as the outer side in the following description.

The rotor 50 has rivets 54, or coupling members that couple the magnetic steel sheets 51 and the first and second holding plates 52, 53 together. Each rivet 54 includes a barrel 54 a and first and second heads 54 b, 54 c. The barrel 54 a is inserted through the magnetic steel sheets 51 and the first and second holding plates 52, 53. The first and second heads 54 b, 54 c are provided at the opposite ends in the axial direction Z of the barrel 54 a. One of the first and second heads 54 b, 54 c is formed in advance before the swaging process and the other is formed by crushing the distal end of the barrel 54 a by swaging.

The magnetic steel sheets 51 and the first and second holding plates 52, 53 are coupled together by being held between the first and second heads 54 b, 54 c. Specifically, the magnetic steel sheets 51 and the first and second holding plates 52, 53 have through-holes 51 a, 52 a, 52 a, which extend therethrough in the axial direction Z of the rotary shaft 12. These through-holes 51 a, 52 a, 53 a have the same shape and communicate with each other in the axial direction Z of the rotary shaft 12. The barrels 54 a are inserted through the through-holes 51 a, 52 a, 53 a. The first and second heads 54 b, 54 c have greater diameters than those of the through-holes 51 a, 52 a, 53 a. The holding plates 52, 53 have holding inner surfaces 52 b, 53 b, which contact the magnetic steel sheets 51. The first and second heads 54 b, 54 c are caught on holding outer surfaces 52 c, 53 c on the side opposite to the holding inner surfaces 52 b, 53 b. As a result, the magnetic steel sheets 51 and the first and second holding plates 52, 53 are unitized. The first and second holding plates 52, 53 are fixed to the rotary shaft 12 so as to rotate integrally with the rotary shaft 12. Therefore, as the rotary shaft 12 rotates, the magnetic steel sheets 51 and the first and second holding plates 52, 53 rotate integrally. In this case, the first and second heads 54 b, 54 c protrude from the first and second holding outer surfaces 52 c, 53 c.

As shown in FIG. 1, the rivets 54 are spaced apart from each other in the circumferential direction of the rotary shaft 12 in the present embodiment. The first holding outer surface 52 c corresponds to a plate surface of a first holding plate, and the second holding outer surface 53 c corresponds to a plate surface of a second holding plate.

As shown in FIG. 2, the rotor 50 has first and second spacers 55, 56, which are provided outward of the first and second holding plates 52, 53 in the axial direction Z of the rotary shaft 12. The first and second spacers 55, 56 are shaped as discs the thickness direction of which coincides with the axial direction Z of the rotary shaft 12. The diameter of the first and second spacers 55, 56 is equal to that of the magnetic steel sheets 51 and the first and second holding plates 52, 53. The thickness of the first and second spacers 55, 56 is greater than that of the first and second heads 54 b, 54 c.

The first spacer 55 has a first contact surface 55 a, which contacts the first holding outer surface 52 c. The surface of the first spacer 55 on the side opposite to the first contact surface 55 a constitutes the first rotor end face 50 a.

The second spacer 56 has a second contact surface 56 a, which contacts the second holding outer surface 53 c. The surface of the second spacer 56 on the side opposite to the second contact surface 56 a constitutes the second rotor end face 50 b.

The first and second spacers 55, 56 have first and second recesses 55 b, 56 b as accommodating portions that accommodate the first and second heads 54 b, 54 c. The first recess 55 b corresponds to a first accommodating portion, and the second recess 56 b corresponds to a second accommodating portion. The first and second recesses 55 b, 56 b are recessed from the first and second contact surfaces 55 a, 56 a toward the outer sides in the axial direction Z. The depth of the first and second recesses 55 b, 56 b is set to be within the range less than the thickness of the first and second spacers 55, 56 and greater than the thickness of the first and second heads 54 b, 54 c. Therefore, the first and second rotor end faces 50 a, 50 b are flat surfaces on which no recesses corresponding to the first and second recesses 55 b, 56 b are formed.

The first and second spacers 55, 56 are fixed to the first and second holding plates 52, 53 with the first and second heads 54 b, 54 c accommodated in the first and second recesses 55 b, 56 b and the first and second contact surfaces 55 a, 56 a contacting the first and second holding outer surfaces 52 c, 53 c. The first and second holding plates 52, 53 and the first and second spacers 55, 56 may be fixed together by any suitable means such as adhesion and engagement.

The first rotor end face 50 a is configured to be smoother than the plate surfaces of the magnetic steel sheets 51 and the plate surface of the first holding plate 52 (more specifically, the first holding outer surface 52 c), and the second rotor end face 50 b is configured to be smoother than the plate surfaces of the magnetic steel sheets 51 and the plate surface of the second holding plate 53 (more specifically, the second holding outer surface 53 c). In other words, the surface roughness (for example, the arithmetic average roughness) of the first and second rotor end faces 50 a, 50 b is less than that of the first and second holding outer surfaces 52 c, 53 c.

A method for manufacturing the rotor 50 according to the present embodiment will be briefly described. The method for manufacturing the rotor 50 includes a lamination step of laminating the magnetic steel sheets 51 and the first and second holding plates 52, 53 and an insertion step of inserting the barrels 54 a of the rivets 54 into the laminated body. Each rivet 54 in the insertion step only has the head is provided at one end of the opposite ends in the axial direction Z of the barrel 54 a.

The method for manufacturing the rotor 50 further includes a swaging step of coupling the laminated body together by crushing the distal end of the barrel 54 a of the rivet 54 (specifically, the end in the axial direction Z of the barrel 54 a opposite to the head). By this swaging step, a head is formed at the distal end of the barrel 54 a, so that the first and second heads 54 b, 54 c are formed at the opposite ends in the axial direction Z of the barrel 54 a.

Thereafter, the method for manufacturing the rotor 50 includes a step of attaching and fixing the first and second spacers 55, 56 to the first and second holding plates 52, 53. In this process, the first and second spacers 55, 56 are attached to the first and second holding plates 52, 53 such that the first and second heads 54 b, 54 c are accommodated in the first and second recesses 55 b, 56 b of the first and second spacers 55, 56.

As shown in FIG. 1, the electric motor 13 includes a stator 57, which is arranged outward of the rotor 50 in the radial direction of the rotary shaft 12 and fixed to the motor housing 41. The rotor 50 and the stator 57 are arranged on the same axis as the rotary shaft 12 and face each other in the radial direction of the rotary shaft 12. The stator 57 has a cylindrical stator core 58 and a coil 59 wound around the stator core 58. As a current flows through the coil 59, the rotor 50 and the rotary shaft 12 rotate integrally.

The motor housing 41 also has a second suction port 60. The second suction port 60 is located closer to the end plate 42 than to the electric motor 13 in the motor housing 41. As fluid flows in from the second suction port 60, the motor chamber A3 is filled with the fluid.

The centrifugal compressor 10 includes an inverter 61 as a drive circuit that drives the electric motor 13 and an inverter case (circuit case) 62 used to define an inverter chamber (circuit chamber) A4 that accommodates the inverter 61. The inverter case 62 has a tubular shape with one end open and the other end closed and is attached to the housing 11 from the axial direction Z of the rotary shaft 12. The end plate 42 has a second plate surface 42 b, which is on the side opposite to the first plate surface 42 a. The open end of the inverter case 62 and the second plate surface 42 b of the end plate 42 abut against each other, and the opening of the inverter case 62 is closed by the end plate 42. The inverter chamber A4 is defined by the inverter case 62 and the end plate 42. The inverter chamber A4 and the motor chamber A3 are partitioned from each other by an end plate 42. In other words, the end plate 42 functions as a partition wall that partitions the motor chamber A3 and the inverter chamber A4 from each other.

This configuration allows the inverter 61 and the fluid in the motor chamber A3 to exchange heat via the end plate 42. Therefore, the heat generated in the inverter 61 is transferred to the motor chamber A3 through the end plate 42 and absorbed by the fluid in the motor chamber A3.

As shown in FIG. 1, first and second bosses 71, 72, through which the rotary shaft 12 (specifically, the main body 12 a) extends, are provided in the motor chamber A3 in the housing 11. The first and second bosses 71, 72 make a pair. The first and second bosses 71, 72 have a tubular shape, specifically, a cylindrical shape having an inner diameter greater than the outer diameter of the main body 12 a of the rotary shaft 12 and an outer diameter that is equal to the outer diameter of the rotor 50. The axes of the bosses 71, 72 coincide with the axis of the main body 12 a. The first and second bosses 71, 72 are arranged to face each other in the axial direction Z of the rotary shaft 12 with the rotor 50 in between.

The first boss 71 rises from the first plate surface 42 a of the end plate 42 in the axial direction Z of the rotary shaft 12, specifically toward the first rotor end face 50 a. The distal end face of the first boss 71, specifically the end face of the first boss 71 in the axial direction Z of the rotary shaft 12, is defined as a first boss end face 71 a. The first boss end face 71 a and the first rotor end face 50 a are arranged so as to face each other while being spaced apart from each other in the axial direction Z of the rotary shaft 12. A portion of the main body 12 a of the rotary shaft 12 opposite to the side where the distal end portion 12 b is provided is inserted through the first boss 71.

The second boss 72 rises from the bottom portion 41 a of the motor housing 41 in the axial direction Z of the rotary shaft 12, specifically toward the second rotor end face 50 b. The distal end face of the second boss 72, specifically the end face of the second boss 72 in the axial direction Z of the rotary shaft 12, is defined as a second boss end face 72 a. The second boss end face 72 a and the second rotor end face 50 b are arranged so as to face each other while being spaced apart from each other in the axial direction Z of the rotary shaft 12. A portion of the main body 12 a of the rotary shaft 12 on the side where the distal end portion 12 b is provided is inserted through the second boss 72.

As described above, the bottom through-holes 41 b are arranged at predetermined intervals in the circumferential direction of the rotary shaft 12. Therefore, the bottom portion 41 a of the motor housing 41 and the second boss 72 are unitized via a part where no bottom through-holes 41 b are provided in the portion of the bottom portion 41 a that overlaps with the second boss 72 as viewed from the axial direction Z of the rotary shaft 12.

The bottom through-holes 41 b are arranged across both the portion that overlaps with the second boss 72 as viewed from the axial direction Z of the rotary shaft 12 and the portion surrounding that overlapping portion. Therefore, the fluid in the motor chamber A3 flows to the second impeller chamber A2 through the openings of the bottom through-holes 41 b around the second boss 72.

As shown in FIGS. 1 and 2, the bosses 71, 72 include first and second radial bearings 81, 82, respectively. Specifically, the first and second radial bearings 81, 82 are provided between inner circumferential surfaces 71 b, 72 b of the bosses 71, 72 and outer circumferential surface 12 c of the rotary shaft 12 (more specifically, the main body 12 a) to rotationally support the rotary shaft 12.

The first and second radial bearings 81, 82 are, for example, flexible non-contact type hydrodynamic bearings. For example, the first radial bearing 81, which is arranged between the first boss 71 and the rotary shaft 12, includes a radial top foil 83, which is arranged outward of the outer circumferential surface 12 c of the rotary shaft 12 in the radial direction of the rotary shaft 12. When the rotary shaft 12 rotates, the radial top foil 83 supports the rotary shaft 12 in a non-contact state. The radial top foil 83 is configured to be displaceable in the radial direction of the rotary shaft 12, while being configured not to rotate with rotation of the rotary shaft 12. Specifically, the radial top foil 83 does not have a completely continuous loop shape but has a tubular shape with a part missing. The radial top foil 83 has opposite ends in the circumferential surface, one of which is a fixed end fixed to the inner circumferential surface 71 b of the first boss 71, and the other one of which is a free end that is located on the side opposite to the fixed end and is spaced apart from the fixed end in the circumferential direction. In this case, while being restricted from rotating, the radial top foil 83 is displaceable through elastic deformation so that the clearance is provided between the radial top foil 83 and the outer circumferential surface 12 c of the rotary shaft 12.

The first radial bearing 81 includes a radial bump foil 84, which is arranged outward of the radial top foil 83 in the radial direction of the rotary shaft 12 and elastically supports the radial top foil 83. The radial bump foil 84 has protrusions protruding inward in the radial direction of the rotary shaft 12 and surrounds the radial top foil 83 with the protrusions contacting the radial top foil 83. The radial bump foil 84 elastically supports the radial top foil 83 in a state of being movable in the radial direction of the rotary shaft 12 by causing the protrusions to be crushed or restore the original shapes. A radial clearance 85 exists between the radial top foil 83 and the radial bump foil 84. The radial clearance 85 opens in the axial direction Z of the rotary shaft 12.

With this configuration, when the rotary shaft 12 rotates, the hydrodynamic pressure generated by the rotation of the rotary shaft 12 rotationally supports the rotary shaft 12 in a non-contact state, in which a clearance exists between the radial top foil 83 and the outer circumferential surface 12 c of the rotary shaft 12. The second radial bearing 82, which is provided between the second boss 72 and the rotary shaft 12 operates in the same manner.

As shown in FIGS. 1 and 2, the centrifugal compressor 10 has the first and second thrust bearings 91, 92, which receive the thrust force generated by the rotation of the impellers 14, 15. The thrust bearings 91, 92 are provided in the motor chamber A3 and on the opposite sides of the rotor 50 in the axial direction Z of the rotary shaft 12. Specifically, the first thrust bearing 91 is provided between the first rotor end face 50 a and the first boss end face 71 a, and the second thrust bearing 92 is provided between the second rotor end face 50 b and the second boss end face 72 a.

In the present embodiment, the first and second thrust bearings 91, 92 are non-contact type hydrodynamic bearings, which receive thrust force in a non-contact state in which the hydrodynamic pressure generated by the rotation of the rotor 50 creates clearances between the first and second thrust bearings 91, 92 and the first and second rotor end faces 50 a, 50 b.

The first and second thrust bearings 91, 92 have the same configuration except for being symmetrical. Thus, the first thrust bearing 91 will be described in detail, and a detailed description of the second thrust bearing 92 will be omitted.

The first thrust bearing 91 has the shape of a loop as a whole (in particular, an annular shape). The first thrust bearing 91 has a thrust top foil 93 and a thrust bump foil 94. The thrust top foil 93 is arranged between the first boss end face 71 a and the first rotor end face 50 a at a position closer to the first rotor end face 50 a than to the first boss end face 71 a. The thrust bump foil 94 is arranged between the first rotor end face 50 a and the first boss end face 71 a at a position closer to the first boss end face 71 a than to the first rotor end face 50 a.

The thrust top foil 93 is constituted by arranging, for example, thin sectoral top foil parts in the circumferential direction of the rotary shaft 12, so that the thrust top foil 93 has the shape of a loop as a whole (in particular, an annular shape). The thrust top foil 93 is configured to be displaceable in the axial direction Z of the rotary shaft 12, while being configured not to rotate with rotation of the rotary shaft 12. For example, one end in the circumferential direction of each top foil part is a fixed end fixed to the first boss end face 71 a, while the other end is a free end.

The thrust bump foil 94 is constituted by arranging, for example, sectoral bump foil parts in the circumferential direction of the rotary shaft 12, so that the thrust bump foil 94 has the shape of a loop as a whole (in particular, an annular shape). The bump foil parts have protrusions protruding in the axial direction Z of the rotary shaft 12 and are fixed to the first boss end face 71 a with the protrusions contacting the thrust top foil 93 (more specifically, the top foil parts). The thrust bump foil 94 elastically supports the thrust top foil 93 in a state of being movable in the axial direction Z of the rotary shaft 12 by causing the protrusions to be crushed or restore the original shapes. A thrust clearance 95 exists between the thrust top foil 93 and the thrust bump foil 94. The thrust clearance 95 opens in the radial direction of the rotary shaft 12. That is, fluid can flow between the inside and the outside of the first thrust bearing 91 in the radial direction through the thrust clearance 95.

With this configuration, when the rotary shaft 12 rotates, the rotor 50 is supported by the first thrust bearing 91 (specifically, the thrust top foil 93) in a non-contact state, in which a clearance exists between the thrust top foil 93 and the first rotor end face 50 a by hydrodynamic pressure. In this case, the first thrust bearing 91 receives the thrust force acting in the axial direction Z of the rotary shaft 12.

The outer diameter of the first thrust bearing 91, in particular, the outer diameter of the thrust top foil 93 and the thrust bump foil 94, is set to be equal to the outer diameter of the rotor 50 and the first boss 71. The inner diameter of the first thrust bearing 91, in particular, the inner diameter of the thrust top foil 93 and the thrust bump foil 94, is set to be greater than the outer diameter of the main body 12 a of the rotary shaft 12. Therefore, an inner space A5, which communicates with the thrust clearance 95, is provided inward of the first thrust bearing 91 in the radial direction of the rotary shaft 12, specifically, between the first thrust bearing 91 and the rotary shaft 12. The first radial bearing 81 includes opposite ends in the axial direction Z, one of which is closer to the first rotor end face 50 a and exposed to the inner space A5 of the first thrust bearing 91. That is, the thrust clearance 95 and the radial clearance 85 communicate with each other through the inner space A5 of the first thrust bearing 91. The inner space A5 corresponds to a space provided inward of the thrust bearing in the radial direction of the rotary shaft.

As shown in FIG. 2, the inner diameter of the first thrust bearing 91 is set to be smaller than the inner diameter of the first boss 71 in the present embodiment. In other words, the first thrust bearing 91 has an inner edge 91 a, which separates from the outer circumferential surface 12 c of the rotary shaft 12 and protrudes further inward than the inner circumferential surface 71 b of the first boss 71 in the radial direction of the rotary shaft 12.

As shown in FIG. 1, the centrifugal compressor 10 constitutes part of a vehicle air conditioner 100. That is, the fluid to be compressed in the centrifugal compressor in the present embodiment is refrigerant.

In addition to the centrifugal compressor 10, the vehicle air conditioner 100 also includes a condenser 101, a gas-liquid separator 102, an expansion valve 103, and an evaporator 104. The condenser 101, the gas-liquid separator 102, the expansion valve 103, and the evaporator 104 are connected together via piping. Also, the condenser 101 is connected to the first discharge port 33, and the evaporator 104 is connected to the second suction port 60. The vehicle air conditioner 100 also has a pipe 105 that connects the second discharge port 36 and the first suction port 30 to each other.

Next, as an operation of the present embodiment, the flow of fluid in the centrifugal compressor 10 and the vehicle air conditioner 100 configured as described above will be described.

When the impellers 14, 15 rotate with rotation of the rotary shaft 12, relatively low-pressure fluid (hereinafter, referred to as suction fluid) discharged from the evaporator 104 is drawn in from the second suction port 60. In this case, the motor chamber A3 is a low-pressure space. The suction fluid drawn into the motor chamber A3 moves toward the second impeller chamber A2. Then, the suction fluid is routed from the second impeller chamber A2 to the second discharge chamber 35 through the second diffuser passage 34 by the centrifugal action of the second impeller 15, and is discharged from the second discharge port 36. The pressure of the fluid present in the second discharge chamber 35 is higher than the pressure of the suction fluid. The fluid discharged from the second discharge port 36 is referred to as an intermediate-pressure fluid.

Some of the suction fluid in the motor chamber A3 is supplied to the first and second thrust bearings 91, 92 provided between the first and second rotor end faces 50 a, 50 b and the first and second boss end faces 71 a, 72 a, and is supplied to the first and second radial bearings 81, 82 through the thrust clearance 95 of the first and second thrust bearings 91, 92 and the inner space A5. In such a situation, rotation of the rotary shaft 12 generates hydrodynamic pressure in the first and second thrust bearings 91, 92 and the first and second radial bearings 81, 82. As a result, the rotary shaft 12 is supported in a non-contact state both in the radial direction and the axial direction Z of the rotary shaft 12. In this case, the first and second thrust bearings 91, 92 receive thrust force.

In addition, as shown in FIG. 1, the intermediate-pressure fluid is drawn into the first suction port 30 via the pipe 105. The intermediate-pressure fluid is routed from the first impeller chamber A1 to the first discharge chamber 32 through the first diffuser passage 31 by the centrifugal action of the first impeller 14, and is discharged from the first discharge port 33. The pressure of the fluid discharged from the first discharge port 33 is higher than the pressure of the intermediate-pressure fluid.

The present embodiment, which has been described above, achieves the following advantages.

(1) The centrifugal compressor 10 includes the rotary shaft 12, the rotor 50 attached to the rotary shaft 12, the electric motor 13, which rotates the rotary shaft 12, the impellers 14, 15, which rotate as the rotary shaft 12 rotates to compress fluid, and the housing 11, which accommodates the rotary shaft 12, the electric motor 13, and the impellers 14, 15. In addition, the centrifugal compressor 10 is provided in the housing 11 and includes the first and second bosses 71, 72, through which the rotary shaft 12 extends.

The first radial bearing 81, which rotationally supports the rotary shaft 12, is arranged between the first boss 71 and the rotary shaft 12. The second radial bearing 82, which rotationally supports the rotary shaft 12, is arranged between the second boss 72 and the rotary shaft 12.

The rotor 50 has first and second rotor end faces 50 a, 50 b, which are positioned on the opposite sides in the axial direction Z of the rotary shaft 12. In the axial direction Z of the rotary shaft 12, the first rotor end face 50 a faces the first boss end face 71 a, which is the end face of the first boss 71 in the axial direction Z of the rotary shaft 12. In the axial direction Z of the rotary shaft 12, the second rotor end face 50 b faces the second boss end face 72 a, which is the end face of the second boss 72 in the axial direction Z of the rotary shaft 12.

The first and second thrust bearings 91, 92, which receive thrust force, are arranged between the first and second rotor end faces 50 a, 50 b and the first and second boss end faces 71 a, 72 a.

With this configuration, the rotor 50 functions as a thrust liner that supports the first and second thrust bearings 91, 92. This configuration provides a dedicated thrust liner and reduces the windage loss as compared with a configuration in which the rotor 50 and the thrust liner both rotate. This increases the efficiency.

Also, in order to suppress wear, a space is normally provided between the rotor 50, which rotates, and the first and second bosses 71, 72, which do not rotate. This space is likely to become a dead space. In this regard, the present embodiment provides the first and second thrust bearings 91, 92 between the rotor 50 and the first and second bosses 71, 72, respectively, so that the dead space is effectively utilized. Further, since it is unnecessary to provide a dedicated chamber for accommodating the first and second thrust bearings 91, 92 and the thrust liner, the size of the centrifugal compressor 10 is reduced.

(2) Further, in a configuration in which a thrust liner is provided at the proximal end of the rotary shaft 12, the assembling directions at the time of manufacture include two directions: the direction from first and second impellers 14, 15 toward the electric motor 13 and the direction opposite to the first direction. In contrast, the present embodiment has only one assembling direction, which is a direction from the first and second impellers 14, 15 toward the electric motor 13. This facilitates the manufacture of the centrifugal compressor 10.

(3) The first and second thrust bearings 91, 92 are respectively provided on the opposite sides of the rotor 50 in the axial direction Z of the rotary shaft 12. Specifically, the first and second bosses 71, 72 are arranged to face each other in the axial direction Z of the rotary shaft 12 with the rotor 50 in between. The first thrust bearing 91 is provided between the first boss end face 71 a of the first boss 71 and the first rotor end face 50 a, which face each other in the axial direction Z of the rotary shaft 12. Also, the second thrust bearing 92 is provided between the second boss end face 72 a of the second boss 72 and the second rotor end face 50 b, which face each other in the axial direction Z of the rotary shaft 12.

This configuration is capable of receiving both the thrust force in a first direction from the first thrust bearing 91 toward the second thrust bearing 92 and the thrust force in a second direction, which is the opposite direction to the first direction.

(4) The rotor 50 includes the magnetic steel sheets 51 laminated in the axial direction Z of the rotary shaft 12, the first and second holding plates 52, 53 holding the magnetic steel sheets 51 in between in the axial direction Z of the rotary shaft 12, and the rivets 54 coupling the magnetic steel sheets 51 and the first and second holding plates 52, 53 together. Each rivet 54 includes a barrel 54 a and first and second heads 54 b, 54 c. The barrel 54 a is inserted through the magnetic steel sheets 51 and the first and second holding plates 52, 53. The first and second heads 54 b, 54 c are provided at the opposite ends in the axial direction Z of the rotary shaft 12 in of the barrel 54 a.

The rotor 50 includes the first and second spacers 55, 56. The first and second spacers 55, 56 have the first and second contact surface 55 a, 56 a, which contact the holding outer surfaces 52 c, 53 c of the first and second holding plates 52, 53, and the first and second rotor end faces 50 a, 50 b, which are arranged on the side opposite to the first and second contact surfaces 55 a, 56 a.

Further, the first and second spacers 55, 56 have the first and second recesses 55 b, 56 b as first and second accommodating portions, in which the first and second heads 54 b, 54 c are accommodated. With this configuration, the first and second thrust bearings 91, 92 are respectively arranged between the first and second spacers 55, 56 and the first and second bosses 71, 72.

In this case, the first and second heads 54 b, 54 c of the rivets are accommodated in the first and second recesses 55 b, 56 b. As a result, the first and second heads 54 b, 54 c are unlikely to interfere with the first and second thrust bearings 91, 92.

Therefore, in the configuration in which the magnetic steel sheets 51 and the holding plates 52, 53 are coupled together by the rivets 54, the first and second thrust bearings 91, 92 are installed in a favorable manner.

Particularly, in a case of the thrust bearings 91, 92, which are non-contact type hydrodynamic bearings that receive thrust force generated during rotation of the rotor 50 in a non-contact state, turbulence caused by the heads 54 b, 54 c in the flow of fluid generated by the rotation of the rotor 50 prevents thrust force from being properly received.

In contrast, in the present embodiment, since the first and second heads 54 b, 54 c are accommodated in the first and second recesses 55 b, 56 b, the first and second heads 54 b, 54 c are unlikely to cause turbulence. This configuration prevents thrust force from being received in an improper manner due to the structure of coupling the magnetic steel sheets 51 and the first and second holding plates 52, 53 together.

(5) It is also conceivable to form recesses, for example, in the first and second holding plates 52, 53. However, due to the characteristics of the rivet 54, it is necessary to perform swaging to crush the distal ends of the inserted barrel 54 a to form heads. If the first and second holding plates 52, 53 had recesses, the swaging process would be difficult to perform, and the coupling (swaging) by the rivets 54 would be likely to be insufficient.

In contrast, the configuration of the present embodiment includes the first and second spacers 55, 56 separately from the first and second holding plates 52, 53. Thus, the first and second spacers 55, 56 can be attached after the above-mentioned swaging process. This eliminates the above-described drawbacks.

(6) The magnetic steel sheets 51 and the first and second spacers 55, 56 are annular as viewed from the axial direction Z of the rotary shaft 12. The first and second thrust bearings 91, 92 are annular and overlapped with the first and second spacers 55, 56 as viewed from the axial direction Z of the rotary shaft 12.

Since this configuration suppresses variation of the centrifugal force generated in the rotor 50 during rotation depending on the position in the circumferential direction, the rotor 50 is allowed to rotate in a stable manner. Also, since the first and second thrust bearings 91, 92 are annular in accordance with the magnetic steel sheets 51 and the first and second spacers 55, 56, the areas of the first and second thrust bearings 91, 92 can be easily increased as compared with the case of elliptical shapes. This increases the magnitude of the force that can be received by the first and second thrust bearings 91, 92.

(7) The first and second thrust bearings 91, 92 (specifically, the thrust top foil 93) are non-contact type hydrodynamic bearings, which receive thrust force in a non-contact state in which the hydrodynamic pressure generated by the rotation of the rotor 50 creates clearances between the first and second thrust bearings 91, 92 and the first and second rotor end faces 50 a, 50 b. In this case, if recesses and protrusions were provided on the first and second rotor end faces 50 a, 50 b, the recesses and protrusions could cause turbulence in the flow of fluid that would generate hydrodynamic pressure between the first and second rotor end faces 50 a, 50 b and the first and second thrust bearings 91, 92. This would disadvantageously lower the hydrodynamic pressure.

In contrast, the first and second rotor end faces 50 a, 50 b of the present embodiment are smoother than the plate surfaces of the first and second holding plates 52, 53 (specifically, the first and second holding outer surfaces 52 c, 53 c). This eliminates the above-described drawbacks and thus allows the first and second thrust bearings 91, 92 to operate in a favorable manner.

(8) The first and second thrust bearings 91, 92 have the thrust top foils 93, which are arranged at positions closer to the first and second rotor end faces 50 a, 50 b than to the first and second boss end faces 71 a, 72 a. The thrust top foils 93 support the rotor 50 in a non-contact state when the rotary shaft 12 rotates.

The first and second thrust bearings 91, 92 have the thrust bump foils 94, which are arranged at positions closer to the first and second boss end faces 71 a, 72 a than to the first and second rotor end faces 50 a, 50 b. The thrust bump foils 94 are elastically deformed to support the thrust top foils 93 in a displaceable manner in the axial direction Z of the rotary shaft 12. This configuration allows the thrust bump foils 94 to be elastically deformed, so that the thrust force is received in a favorable manner.

Also, when vibration in the axial direction Z of the rotary shaft 12 occurs in the centrifugal compressor 10, the vibration is absorbed by elastic deformation of the thrust bump foils 94. This configuration restricts sliding contact between the first and second rotor end faces 50 a, 50 b and the first and second boss end faces 71 a, 72 a due to the vibration in the axial direction Z of the rotary shaft 12. The vibration is thus dealt with in a favorable manner.

(9) The first and second radial bearings 81, 82 each have a radial top foil 83, which is provided outward of the outer circumferential surface 12 c of the rotary shaft 12 in the radial direction of the rotary shaft 12, and a radial bump foil 84, which is provided outward of the radial top foil 83 in the radial direction of the rotary shaft 12. The radial top foils 83 support the rotary shaft 12 in a non-contact state when the rotary shaft 12 rotates. The radial bump foils 84 elastically support the radial top foils 83. The first and second thrust bearings 91, 92 are shaped as a loop having an inner diameter longer than the diameter of the rotary shaft 12. The inner space A5 is provided inward of the first and second thrust bearings 91, 92 in the radial direction of the rotary shaft 12.

In this configuration, the radial clearance 85, which is open in the axial direction Z of the rotary shaft 12 in the first radial bearing 81, and the thrust clearance 95, which is opened in the radial direction of the rotary shaft 12 in the first thrust bearing 91, communicate with each other through the inner space A5 of the first thrust bearing 91.

As a result, the fluid in the motor chamber A3 (the suction fluid in the present embodiment) is supplied to the first radial bearing 81 via the thrust clearance 95 of the first thrust bearing 91 and the inner space A5. Thus, when the rotary shaft 12 rotates, the necessary hydrodynamic pressure is generated in the first radial bearing 81.

Thus, the configuration eliminates the drawback caused by the first thrust bearing 91 being arranged between the first boss end face 71 a and the first rotor end face 50 a. Specifically, it is possible to prevent the first thrust bearing 91 from restricting the supply of fluid to the first radial bearing 81, so that the operation of the first radial bearing 81 will not be hampered. The second radial bearing 82 and second thrust bearing 92 achieve the same advantage.

(10) Particularly, the first thrust bearing 91 has an inner edge 91 a, which separates from the outer circumferential surface 12 c of the rotary shaft 12 and protrudes further inward than the inner circumferential surface 71 b of the first boss 71 in the radial direction of the rotary shaft 12. Since this configuration increases the area of the first thrust bearing 91, the receivable thrust force is increased. The second thrust bearing 92 achieves the same advantage.

(11) The centrifugal compressor 10 includes the inverter 61, which drives the electric motor 13, and the inverter case 62, which defines the inverter chamber A4. The inverter chamber A4 accommodates the inverter 61. The inverter case 62 is attached to the housing 11 in the axial direction Z of the rotary shaft 12. The housing 11 includes the motor chamber A3, which accommodates the electric motor 13 and into which fluid is drawn from the second suction port 60, and the end plate 42, which functions as a partition wall partitioning the motor chamber A3 and the inverter chamber A4 from each other.

This configuration allows the inverter 61 to exchange heat with the fluid in the motor chamber A3 via the end plate 42. Accordingly, the inverter 61 can be cooled by using the fluid in the motor chamber A3.

Particularly, the present embodiment has no thrust chamber that accommodates a thrust bearing and a thrust liner between the inverter chamber A4 and motor chamber A3. Accordingly, the inverter 61 can be cooled by using the fluid in the motor chamber A3 in a favorable manner. This suppresses the generation of heat by the inverter 61.

(12) The centrifugal compressor 10 includes the first impeller 14 and the second impeller 15, which are arranged such that the end faces 14 a, 15 a face each other. The suction fluid is drawn into the motor chamber A3 from the second suction port 60. In addition, the motor chamber A3 communicates with the second impeller chamber A2, which accommodates the second impeller 15, and the second impeller 15 compresses the suction fluid, which has been drawn into the second impeller chamber A2 from the motor chamber A3. The first impeller 14 is configured to compress the intermediate-pressure fluid, which has been compressed by the second impeller 15.

This configuration fills the motor chamber A3 with the suction fluid, the pressure of which is relatively low. This reduces the windage loss of the rotor 50 provided in the motor chamber A3.

The above-described embodiment may be modified as follows.

As shown in FIG. 3, the first discharge port 33 and the second suction port 60 may be omitted. In this case, the centrifugal compressor 10 may include an intermediate pressure port 110, which connects the first discharge chamber 32 and the motor chamber A3 to each other. The intermediate pressure port 110 extends in the radial direction Z of the rotary shaft 12 through the middle part 23, the second part 22, and the bottom portion 41 a of the motor housing 41. Also, the condenser 101 is connected to the second discharge port 36, and the first suction port 30 is connected to the evaporator 104.

In this configuration, the fluid that is discharged from the evaporator 104 and drawn from the first suction port 30 is discharged from the second discharge port 36 after passing through the first impeller chamber A1, the first diffuser passage 31, the first discharge chamber 32, the intermediate pressure port 110, the motor chamber A3, the second impeller chamber A2, the second diffuser passage 34, and the second discharge chamber 35 in the order. In this case, the motor chamber A3 is filled with the intermediate-pressure fluid.

Either one of the first and second thrust bearings 91, 92 may be omitted.

The first and second thrust bearings 91, 92 may have different structures.

The first boss 71 may have a through-hole extending therethrough in the radial direction of the rotary shaft 12. This through-hole preferably connects the space between the first radial bearing 81 and the end plate 42 to the space on the outer side of the first boss 71 in the radial direction of the rotary shaft 12. This allows fluid to be supplied to the first radial bearing 81 in a more favorable manner.

The outer diameter of the rotor 50 may be different from the outer diameter of the first and second bosses 71, 72. In this case, the outer diameter of the thrust bearing 91, 92 is preferably shorter than or equal to the shorter of the outer diameter of the rotor 50 and the outer diameter of the first and second bosses 71, 72.

Further, the inner diameter of the first and second thrust bearings 91, 92 may be set to be greater than or equal to the inner diameter of the first and second bosses 71, 72.

The magnetic steel sheets 51 may be non-annular as viewed from the axial direction Z of the rotary shaft 12. This increases the saliency of the rotor 50. In this configuration, the spacers 55, 56 are preferably annular as viewed from the axial direction Z of the rotary shaft 12. This allows the first and second thrust bearings 91, 92 to receive thrust force in a favorable manner, while increasing the saliency of the rotor 50.

The present invention is not limited this, but the first and second holding plates 52, 53 and the first and second spacers 55, 56 may also be non-annular in correspondence with the shape of the magnetic steel sheets 51. Also, the bosses 71, 72 may have a tubular shape that is non-circular as viewed from the axial direction Z of the shaft 12.

The first and second spacers 55, 56 may be omitted. In this case, the first and second holding outer surfaces 52 c, 53 c of the first and second holding plates 52, 53 constitute the first and second rotor end faces 50 a, 50 b. Also, the first and second holding outer surfaces 52 c, 53 c of the first and second holding plates 52, 53 may have recesses that accommodate the first and second heads 54 b, 54 c. Further, only one of the first and second spacers 55, 56 may be omitted.

The accommodating portions are not limited to recesses, but may be through-holes extending through the first and second spacers 55, 56 in the thickness direction.

Other than the rivets 54, any configuration may be used to couple the magnetic steel sheets 51 and the first and second holding plates 52, 53 together and cause these to rotate integrally with the rotor 50. In short, any configuration may be employed as long as the magnetic steel sheets 51 and the first and second holding plates 52, 53 are fixed to the rotary shaft 12 so as to rotate integrally with the rotor 50 while being coupled together.

In the above-described embodiment, the first and second thrust bearings 91, 92 are of a foil type having the thrust top foils 93 and the thrust bump foils 94. The present invention is not limited this, and any configuration can be employed as long as thrust force can be received. The same applies to the radial bearings 81, 82.

Either one of the first and second impellers 14, 15 may be omitted. In this case, the diffuser passage and the discharge chamber that correspond to the omitted impeller may be omitted.

The centrifugal compressor 10 may be mounted on any structure other than a vehicle.

In the above-described embodiment, the centrifugal compressor 10 is used as a part of the vehicle air conditioner 100. The present invention is not limited to this, and the compressor 10 may be used for other purposes. For example, if the vehicle is a fuel cell vehicle (FCV), which mounts a fuel cell, the centrifugal compressor 10 may be used in a supplying device that supplies air to the fuel cell. That is, the fluid to be compressed may be any fluid such as refrigerant or air. The fluid device is not limited to the vehicle air conditioner 100, but may be any device. 

1. A centrifugal compressor comprising: a rotary shaft; an electric motor, which includes a rotor attached to the rotary shaft and rotates the rotary shaft; an impeller, which rotates as the rotary shaft rotates, thereby compressing fluid; a housing, which accommodates the rotary shaft, the electric motor, and the impeller; a tubular boss, which is provided in the housing and through which the rotary shaft extends; and a radial bearing, which is provided between the boss and the rotary shaft and rotationally supports the rotary shaft, wherein the rotor has a rotor end face, which is an end face in an axial direction of the rotary shaft, the boss has a boss end face, which is an end face in the axial direction of the rotary shaft, the rotor end face and the boss end face face each other in the axial direction of the rotary shaft, and the centrifugal compressor comprises a thrust bearing, which is arranged between the rotor end face and the boss end face and receives thrust force generated by rotation of the impeller.
 2. The centrifugal compressor according to claim 1, wherein the boss is a first boss, the centrifugal compressor further comprises a second boss, which makes a pair with the first boss, the first boss and the second boss are arranged to face each other in the axial direction of the rotary shaft with the rotor in between, the rotor has a first rotor end face as the rotor end face and a second rotor end face, which is located on a side opposite to the first rotor end face in the axial direction of the rotary shaft, the first boss has a first boss end face as the boss end face, the first boss end face and the first rotor end face facing each other in the axial direction of the rotary shaft, the second boss has a second boss end face as the boss end face, the second boss end face and the second rotor end face facing each other in the axial direction of the rotary shaft, the thrust bearing is a first thrust bearing provided between the first rotor end face and the first boss end face, and the centrifugal compressor further comprises a second thrust bearing provided between the second rotor end face and the second boss end face.
 3. The centrifugal compressor according to claim 2, wherein the rotor includes a plurality of magnetic steel sheets, which is laminated in the axial direction of the rotary shaft, first and second holding plates, which hold the magnetic steel sheets in between in the axial direction of the rotary shaft, a rivet, which includes a barrel and first and second heads, wherein the barrel is inserted through the magnetic steel sheets and the first and second holding plates, and the first and second heads have a diameter greater than that of the barrel and are arranged at opposite ends of the barrel in the axial direction of the rotary shaft, a first spacer, which has a first contact surface contacting a plate surface of the first holding plate, the first rotor end face, which is arranged on a side opposite to the first contact surface, and a first accommodating portion, which accommodates the first head, and a second spacer, which has a second contact surface contacting a plate surface of the second holding plate, the second rotor end face, which is arranged on a side opposite to the second contact surface, and a second accommodating portion, which accommodates the second head.
 4. The centrifugal compressor according to claim 3, wherein the first thrust bearing is a non-contact type hydrodynamic bearing, which receives the thrust force in a non-contact state in which hydrodynamic pressure generated by rotation of the rotor creates a clearance between the first thrust bearing and the first rotor end face, the second thrust bearing is a non-contact type hydrodynamic bearing, which receives the thrust force in a non-contact state in which hydrodynamic pressure generated by rotation of the rotor creates a clearance between the second thrust bearing and the second rotor end face, and the first rotor end face and the second rotor end face are smoother than the plate surfaces of the first and second holding plates.
 5. The centrifugal compressor according to claim 1, wherein the thrust bearing includes a thrust top foil, which is arranged between the boss end face and the rotor end face at a position closer to the rotor end face than to the boss end face and supports the rotor in a non-contact state when the rotary shaft rotates, and a thrust bump foil, which is arranged between the boss end face and the rotor end face at a position closer to the boss end face than to the rotor end face and is elastically deformed to support the thrust top foil in a displaceable manner in the axial direction of the rotary shaft.
 6. The centrifugal compressor according to claim 5, wherein the radial bearing includes a radial top foil, which is arranged outward of an outer circumferential surface of the rotary shaft in a radial direction of the rotary shaft and supports the rotary shaft in a non-contact state when the rotary shaft rotates, and a radial bump foil, which is arranged outward of the radial top foil in the radial direction of the rotary shaft and elastically supports the radial top foil, wherein the thrust bearing has a shape of a loop having an inner diameter longer than a diameter of the rotary shaft, a space is provided inward of the thrust bearing in the radial direction of the rotary shaft, and the space causes a radial clearance, which is provided between the radial top foil and the radial bump foil, and a thrust clearance, which is provided between the thrust top foil and the thrust bump foil, to communicate with each other.
 7. The centrifugal compressor according to claim 1, further comprising: a drive circuit, which drives the electric motor; and a circuit case, which defines a circuit chamber that accommodates the drive circuit and is attached to the housing from the axial direction of the rotary shaft, wherein the housing includes a motor chamber, which accommodates the electric motor and into which fluid is drawn, and a partition wall, which partitions the motor chamber and the circuit chamber from each other, and the drive circuit exchanges heat with the fluid in the motor chamber via the partition wall.
 8. The centrifugal compressor according to claim 6, wherein an inner edge of the thrust bearing protrudes further inward than an inner circumferential surface of the boss in the radial direction of the rotary shaft. 